Fire-Safe Decking

A.Stephen Quarles, a
University of California Cooperative Extension
advisor in Richmond, Calif., responds: For
truly noncombustible decking, you could use an
aluminum product like AridDek
(ariddek.com),
Last-Deck
(lastdeck.com),
or Lock Dry
(lockdry.com).
But there aren’t currently any wood,
plastic, or wood-plastic composite deck boards that
have a noncombustible rating. Keep in mind, though,
that even in California, where homes built in
wildfire-prone areas must comply with the
state’s stringent, newly adopted fire
code, deck boards don’t have to be
“noncombustible”; they just have
to meet certain minimum performance criteria (see
Chapter 7A of the 2007 California Building
Code).

Those standards — and the fire-test
protocols used to establish them — were
developed by researchers (including myself) at the
University of California Forest Products
Laboratory. We tested several different types of
commercially available plastic and wood-plastic
composite deckboards, as well as solid redwood
decking. To simulate an under-deck surface fire, we
exposed deck boards to an 80-kilowatt propane flame
for three minutes. And to simulate burning embers
landing on the deck, we used an ASTM E-108
“A” brand: a 1-square-foot,
three-layer assembly of nailed-together
3/4-inch-square sticks that we set on fire and
placed on the decking (the same method used to test
roofing).

Our testing showed that a decking
material’s fire performance was largely
dependent on its cross-section (solid, channeled,
or hollow), the plastic component used in its
construction, and the presence or absence of a
fiber reinforcement. Channeled deck boards tended
to perform poorly in the under-deck tests, while
hollow decking typically performed poorly in the
burning-brand tests. Solid decking performed best
overall; it’s worth noting that 2x6
heart-grade redwood, a common decking material in
California, performed as well as or better than all
of the plastic and composite decking products we
tested.

These tests were conducted about eight years
ago, and many of the plastic and composite lumber
manufacturers have since modified how their deck
boards are made in order to comply with the
California requirements. Therefore, how any given
product performed in our original testing
isn’t necessarily an indication of how it
would perform today.

There are several decking products that now meet
the performance standards established by the CBC,
such as TimberTech XLM
(timbertech.com),
a solid PVC product with a Class A flame-spread
rating, and Trex Accents Fire Defense
(trex.com), a
wood-polyethylene composite with a Class B
flame-spread rating. Also approved for use is
nominal 2-by solid-wood decking in several species,
including redwood and some types of cedar.

For a list of these products and information
about the compliance criteria, you can download a
free handbook, “Wildland Urban Interface
Products,” at
jlconline.com/firetested.
Some of the products aren’t easy to find
outside of California, but they may be available
through special order at your local lumberyard.